The invention relates to a hydraulic damping cylinder, in particular for a prosthetic knee joint, comprising a housing, a cylinder chamber which is provided in the housing and which is filled with a hydraulic fluid, and a piston which is arranged in said cylinder chamber and which can be moved in the cylinder chamber by way of a piston rod which is introduced into the cylinder chamber.
A hydraulic damping cylinder of said type is used for example in a prosthetic knee joint in order to dampen the flexion movement during which the prosthetic knee joint bends, similarly to the human joint. Said damping is realized in purely fluid mechanical fashion by virtue of the flow of the hydraulic fluid conveyed out of the cylinder chamber into a receiving chamber being correspondingly throttled.
It is also known for a damping cylinder of said type to be equipped with an extension aid. Such an extension aid constitutes an energy store which is charged during the course of the flexion and which, during the course of the extension, that is to say when the prosthetic knee joint is straightened again, is discharged and thereby assists said extension movement. For this purpose, it is known for the damping cylinder to be equipped with a spring element which constitutes the energy store and which is stressed during the course of the flexion and which is relaxed again during the extension. In the case of a damping cylinder of said type, however, the energy storage is purely travel-dependent, that is to say the amount of energy stored in the spring is dependent only on the extent to which the knee joint is bent. That is to say, the stored restoring energy is always the same, regardless of the walking speed of the wearer of the prosthesis, if the prosthetic knee joint is always bent consistently to the same angle during the course of the fast or slow movement. This is however sometimes uncomfortable for the wearer of the prosthesis. This is because, during slow walking, owing to the low step frequency, relatively little extension assistance is sufficient, whereas, during fast walking, owing to the high step frequency, more intense extension assistance would be necessary.